I am afraid that is more of manual procedure, there is migration project but it intended to migrate from jBPM 3.x into 5 but it focuses only on process definition and not running processes. What you will need to do is probably introduce some kind of transitions stage that will run both engines at the same time where new instances will be started on jBPM5 and those that are already running will continue on 4.4 until they reach the end.
HTH